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Materials, Volume 12, Issue 2 (January-2 2019)

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Cover Story (view full-size image) Oxygen evolution reaction (OER) is important reaction for energy conversion. Metal-free [...] Read more.
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Open AccessArticle Behavior of Intermetallic Compounds of Al-Ti Composite Manufactured by Spark Plasma Sintering
Materials 2019, 12(2), 331; https://doi.org/10.3390/ma12020331
Received: 13 December 2018 / Revised: 16 January 2019 / Accepted: 18 January 2019 / Published: 21 January 2019
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Abstract
In this research, we successfully fabricate high-hardness and lightweight Al-Ti composites. Al-Ti composites powders with three compositions (Al-20, 50, and 80 vol.% Ti) are mixed using ball milling and subsequently subjected to spark plasma sintering (SPS). The microstructures and phases of the Al-Ti [...] Read more.
In this research, we successfully fabricate high-hardness and lightweight Al-Ti composites. Al-Ti composites powders with three compositions (Al-20, 50, and 80 vol.% Ti) are mixed using ball milling and subsequently subjected to spark plasma sintering (SPS). The microstructures and phases of the Al-Ti composites are characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD) spectroscopy, and field emission-electron probe microanalysis (FE-EPMA). These tests confirm the presence of several intermetallic compounds (ICs) (Al3Ti, Al5Ti2, Al11Ti5) in the composites, and we are able to confirm that these ICs are produced by the reaction of Al and Ti during the SPS process. Furthermore, thermogravimetric-differential thermal analysis (TG-DTA) is used to analyze the formation behavior of the ICs. In addition, the mechanical properties of the composites are measured using their Vickers hardness and it is observed that the Al-80 vol.% Ti composite exhibits the highest hardness. Consequently, it is assumed that SPS is suitable for fabricating Al-Ti composites which represent the next-generation materials to be used in various industrial fields as high-hardness and lightweight materials. Full article
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Open AccessArticle The Reaction Thermodynamics during Plating Al on Graphene Process
Materials 2019, 12(2), 330; https://doi.org/10.3390/ma12020330
Received: 23 December 2018 / Revised: 15 January 2019 / Accepted: 18 January 2019 / Published: 21 January 2019
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Abstract
This research explored a novel chemical reduction of organic aluminum for plating Al on a graphene surface. The thermodynamics of the Al plating reaction process were studied. The Al plating process consisted of two stages: the first was to prepare (C2H [...] Read more.
This research explored a novel chemical reduction of organic aluminum for plating Al on a graphene surface. The thermodynamics of the Al plating reaction process were studied. The Al plating process consisted of two stages: the first was to prepare (C2H5)3Al. In this reaction, the ΔH(enthalpy) was 10.64 kcal/mol, the ΔG(Gibbs free energy) was 19.87 kcal/mol and the ΔS(entropy) was 30.9 cal/(mol·K); this was an endothermic reaction. In the second stage, the (C2H5)3Al decomposed into Al atoms, which were gradually deposited on the surface of the graphene and the Al plating formed. At 298.15 K, the ΔH was −20.21 kcal/mol, the ΔG was −54.822 kcal/mol, the ΔS was 116.08 cal/(mol·K) and the enthalpy change was negative, thus indicating an endothermic reaction. Full article
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Open AccessArticle Effect of Fibers on High-Temperature Mechanical Behavior and Microstructure of Reactive Powder Concrete
Materials 2019, 12(2), 329; https://doi.org/10.3390/ma12020329
Received: 10 December 2018 / Revised: 27 December 2018 / Accepted: 31 December 2018 / Published: 21 January 2019
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Abstract
This study was aimed to investigate the effect of steel, polypropylene (PP), and hybrid (steel + PP) fibers on high-temperature mechanical properties of reactive powder concrete (RPC). The mechanical properties considered are cubic compressive strength, axial or prismatic compressive strength, split-tensile strength, flexural [...] Read more.
This study was aimed to investigate the effect of steel, polypropylene (PP), and hybrid (steel + PP) fibers on high-temperature mechanical properties of reactive powder concrete (RPC). The mechanical properties considered are cubic compressive strength, axial or prismatic compressive strength, split-tensile strength, flexural strength, elastic modulus, peak strain, and stress-strain behavior. The strength recession due to high temperature was investigated at micro level by scanning electron microscope, energy dispersive X-ray spectroscopy, X-ray diffraction, mercury intrusion porosity, thermogravimetric, and differential scanning calorimetry analyses. The high-temperature tests were carried out at target temperatures of 120, 300, 500, 700, and 900 °C. The hot-state compressive strength of RPC started to decrease at 120 °C; however, a partial recovery at 300 °C and a gradual decrease above 300 °C were observed. The degradation of split-tensile strength, flexural strength, and elastic modulus were gradual with increasing temperature despite the effect of different fibers. Whereas, the peak strain was gradually increasing up to 700 °C. However, after 700 °C, it remained unchanged. Steel fiber reinforced RPC (SRPC) and hybrid fiber reinforced RPC (HRPC) showed a ductile behavior. PP fiber reinforced RPC (PRPC) showed a quite brittle behavior up to 300 °C; however, further heating made the microstructure porous and it became ductile too. Overall the performance of SRPC and HRPC were superior to PRPC because of higher modulus of elasticity, higher strength, and better fire resistance of steel fibers. Fiber reinforced RPC was found to have better fire resistance than traditional types of concrete based on comparative studies with the provisions of design codes and earlier research. The constitutive equations developed can be utilized in computer programs for structural design of RPC structures exposed to fire. Full article
(This article belongs to the Special Issue New and Emerging Construction Materials)
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Open AccessArticle Co-Polymers based on Poly(1,4-butylene 2,5-furandicarboxylate) and Poly(propylene oxide) with Tuneable Thermal Properties: Synthesis and Characterization
Materials 2019, 12(2), 328; https://doi.org/10.3390/ma12020328
Received: 11 December 2018 / Revised: 15 January 2019 / Accepted: 15 January 2019 / Published: 21 January 2019
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Abstract
Poly(ether ester)s (PEEs) represent a promising class of segmented co-polymers, nevertheless the synthesis of PEEs based on renewable 2,5-furandicarboxylic acid (FDCA) is still scarce. In this context, a series of poly(1,4-butylene 2,5-furandicarboxylate)-co-poly(poly(propylene oxide) 2,5-furandicarboxylate) co-polyesters with different composition of stiff poly(1,4-butylene [...] Read more.
Poly(ether ester)s (PEEs) represent a promising class of segmented co-polymers, nevertheless the synthesis of PEEs based on renewable 2,5-furandicarboxylic acid (FDCA) is still scarce. In this context, a series of poly(1,4-butylene 2,5-furandicarboxylate)-co-poly(poly(propylene oxide) 2,5-furandicarboxylate) co-polyesters with different composition of stiff poly(1,4-butylene 2,5-furandicarboxylate) (PBF) and soft poly(poly(propylene oxide) 2,5-furandicarboxylate) (PPOF) moieties were synthesized, via a two-step bulk polytransesterification reaction. The molar ratio of PBF/PPOF incorporated was varied (10 to 50 mol%) in order to prepare several novel materials with tuned properties. The materials were characterised in detail through several techniques, namely ATR FTIR, 1H and 13C NMR, TGA, DSC, DMTA and XRD. Their hydrolytic and enzymatic degradation evaluation was also assessed. These new co-polymers showed either a semi-crystalline nature when higher PBF/PPOF ratios were used, and for approximately equal amounts of PBF and PPOF an amorphous co-polyester was obtained instead. Full article
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Open AccessArticle Stimuli-Responsive Systems in Optical Humidity-Detection Devices
Materials 2019, 12(2), 327; https://doi.org/10.3390/ma12020327
Received: 4 December 2018 / Revised: 20 December 2018 / Accepted: 21 December 2018 / Published: 21 January 2019
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Abstract
The use of electronic devices to measure Relative Humidity (RH) is widespread. However, under certain circumstances, for example when explosive gases are present, a spark-free method should be used. Here we suggest the use of stimuli-responsive materials, like gelatin and interpenetrated polymers, to [...] Read more.
The use of electronic devices to measure Relative Humidity (RH) is widespread. However, under certain circumstances, for example when explosive gases are present, a spark-free method should be used. Here we suggest the use of stimuli-responsive materials, like gelatin and interpenetrated polymers, to detect RH with an optical method. These materials are hydrophilic. When water vapor is absorbed by the films the molecules attach to the films molecular network. The result is that the film thickness increases and their refractive index changes. To detect the change of these two parameters an optical method based on diffraction gratings is employed. Surface diffraction gratings are recorded on the films. Then gratings are placed in an optical configuration that is immersed in a climatic chamber. A light beam is sent to the grating where it is diffracted. Several light orders appear. Due to the absorption of water molecules the films swell and grating surface modulation changes. This implies that the diffracted orders intensity changes. A calibrating plot relating intensity as a function of RH is obtained. Full article
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Open AccessReview Properties of Cement-Based Composites Modified with Magnetite Nanoparticles: A Review
Materials 2019, 12(2), 326; https://doi.org/10.3390/ma12020326
Received: 27 December 2018 / Revised: 8 January 2019 / Accepted: 12 January 2019 / Published: 21 January 2019
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Abstract
Despite the many available studies on the evaluation of the influence of nanomaterials on the properties of cement-based composites, the effects of some nanoparticles have not yet been fully recognized. Among the unrecognized nanomaterials are magnetite nanoparticles (MN). The literature devoted to this [...] Read more.
Despite the many available studies on the evaluation of the influence of nanomaterials on the properties of cement-based composites, the effects of some nanoparticles have not yet been fully recognized. Among the unrecognized nanomaterials are magnetite nanoparticles (MN). The literature devoted to this subject is limited. This paper reviews state-of-the-art research carried out on the effect of MN on the properties of cement-based composites. Detailed descriptions of the processing, microstructures (hydration products), properties (hydration, workability, mechanical and functional properties, and durability), and probability applications of MN-engineered cementitious composites are presented. Particular attention has been paid to MN application methods to the cement composite. Finally, the risks, challenges, and future development of MN-modified cement-based composites is discussed. Full article
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Open AccessCommunication Nonlinear Resonance Vibration Assessment to Evaluate the Freezing and Thawing Resistance of Concrete
Materials 2019, 12(2), 325; https://doi.org/10.3390/ma12020325
Received: 19 December 2018 / Revised: 14 January 2019 / Accepted: 18 January 2019 / Published: 21 January 2019
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Abstract
Under cold environments, the freezing and thawing cycles of water in concrete reduce the lifetime and durability of concrete structures. For enhanced freezing and thawing resistance, entrained air voids are generally required, but malfunctioning of air entrainment is sometimes reported in the field. [...] Read more.
Under cold environments, the freezing and thawing cycles of water in concrete reduce the lifetime and durability of concrete structures. For enhanced freezing and thawing resistance, entrained air voids are generally required, but malfunctioning of air entrainment is sometimes reported in the field. To evaluate the quality of air entrainment, this study proposes a nondestructive method that is a preceding evaluation before damage to the concrete. A nonlinear resonance vibration method is adopted in samples having an identical air void content. The durable concrete sample with resistance to freezing and thawing cycles shows higher nonlinearity in its resonance. Thus, the quality of air entrainment and, furthermore, the potential freezing and thawing resistance can possibly be evaluated by measuring the nonlinearity parameter of the concrete, which is preliminary study to attempt the preceding evaluation of freezing and thawing resistance using nondestructive method. Full article
(This article belongs to the Special Issue Testing of Cement-Based Materials)
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Open AccessArticle The Mix Ratio Study of Self-Stressed Anti-Washout Underwater Concrete Used in Nondrainage Strengthening
Materials 2019, 12(2), 324; https://doi.org/10.3390/ma12020324
Received: 14 December 2018 / Revised: 10 January 2019 / Accepted: 15 January 2019 / Published: 21 January 2019
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Abstract
Anti-washout underwater concrete (AWC) is widely used in nondrainage strengthening; however, there still exist some problems with it, such as high strength loss and poor interfacial bond in practical engineering application. Based on the study of self-stressed concrete (SSC), a research on the [...] Read more.
Anti-washout underwater concrete (AWC) is widely used in nondrainage strengthening; however, there still exist some problems with it, such as high strength loss and poor interfacial bond in practical engineering application. Based on the study of self-stressed concrete (SSC), a research on the mix ratio for the C30 self-stressed anti-washout underwater concrete (SSAWC) was carried out in this paper in hope of solving the above problems, specifically, by adding an expansive agent to the AWC. The parameters, such as strength, fluidity, anti-dispersity, and expansibility, were picked as target indices in determination of the mix ratio. The orthogonal test design and range analysis were used to determine the reasonable mix ratio and study the influence of various parameters on the performance of SSAWC. The experimental program conducted includes a series of strength, fluidity, anti-dispersity, and expansibility tests on 18 groups of specimens. The results show that C30 SSAWC has an excellent performance using the optimal mix ratio. Compared with AWC, the expansibility and self-stress of the SSAWC can be easily observed, and the compressive strength ratio of the SSAWC casted in water to that casted in air is much bigger. This implies that SSAWC is applicable to the nondrainage strengthening. Full article
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Open AccessArticle Iron [email protected] Nanocomposites: A Tool Box of Functional Materials
Materials 2019, 12(2), 323; https://doi.org/10.3390/ma12020323
Received: 23 November 2018 / Revised: 4 January 2019 / Accepted: 8 January 2019 / Published: 21 January 2019
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Abstract
Iron carbide (Fe3C) is a ceramic magnetic material with high potential for applications in different fields, including catalysis, medicine imaging, coatings, and sensors. Despite its interesting properties, it is still somehow largely unexplored, probably due to challenging synthetic conditions. In this [...] Read more.
Iron carbide (Fe3C) is a ceramic magnetic material with high potential for applications in different fields, including catalysis, medicine imaging, coatings, and sensors. Despite its interesting properties, it is still somehow largely unexplored, probably due to challenging synthetic conditions. In this contribution, we present a sol-gel-based method that allows preparing different Fe3[email protected] nanocomposites with tailored properties for specific applications, in particular, we have focused on and discussed potential uses for adsorption of noxious gas and waste removal. Nanocomposites were prepared using readily available and “green” sources, such as urea, simple and complex sugars, and chitosan. The nanocomposite prepared from chitosan was found to be more efficient for CO2 uptake, while the sample synthetized from cellulose had optimal capability for dye absorption and waste oil removal from water. Full article
(This article belongs to the Special Issue Novel Metal Carbide/Carbonitride Materials)
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Open AccessCommunication Highly Transparent, Flexible and Conductive CNF/AgNW Paper for Paper Electronics
Materials 2019, 12(2), 322; https://doi.org/10.3390/ma12020322
Received: 19 December 2018 / Revised: 10 January 2019 / Accepted: 18 January 2019 / Published: 21 January 2019
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Abstract
Conductive paper has the advantages of being low-cost, lightweight, disposable, flexible, and foldable, giving it promising potential in future electronics. However, mainstream conductive papers are opaque and rigid, which seriously affect the wide application of conductive paper. In this paper, we demonstrate a [...] Read more.
Conductive paper has the advantages of being low-cost, lightweight, disposable, flexible, and foldable, giving it promising potential in future electronics. However, mainstream conductive papers are opaque and rigid, which seriously affect the wide application of conductive paper. In this paper, we demonstrate a highly transparent, flexible, and conductive paper, fabricated by mixing cellulose nanofibers (CNFs) with silver nanowires (AgNWs) and then plasticizing with choline chloride/urea solvent. The as-prepared CNF/AgNW paper showed high transparency (~90% transmittance) and flexibility (~27% strain), and low sheet resistance (56 Ω/sq). Moreover, the resistance change of CNF/AgNW paper increased only ~1.1% after 3000 bending−unbending cycles under a 150° large angle, implying a long working life and stability. In view of this, our methodology has the potential to open a new powerful route for fabrication of paper-based green electronics. Full article
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Open AccessArticle The Martensitic Transformation and Mechanical Properties of Ti6Al4V Prepared via Selective Laser Melting
Materials 2019, 12(2), 321; https://doi.org/10.3390/ma12020321
Received: 14 December 2018 / Revised: 17 January 2019 / Accepted: 18 January 2019 / Published: 21 January 2019
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Abstract
This article investigated the microstructure of Ti6Al4V that was fabricated via selective laser melting; specifically, the mechanism of martensitic transformation and relationship among parent β phase, martensite (α’) and newly generated β phase that formed in the present experiments were elucidated. The primary [...] Read more.
This article investigated the microstructure of Ti6Al4V that was fabricated via selective laser melting; specifically, the mechanism of martensitic transformation and relationship among parent β phase, martensite (α’) and newly generated β phase that formed in the present experiments were elucidated. The primary X-ray diffraction (XRD), transmission electron microscopy (TEM) and tensile test were combined to discuss the relationship between α’, β phase and mechanical properties. The average width of each coarse β columnar grain is 80–160 μm, which is in agreement with the width of a laser scanning track. The result revealed a further relationship between β columnar grain and laser scanning track. Additionally, the high dislocation density, stacking faults and the typical ( 10 1 ¯ 1 ) twinning were identified in the as-built sample. The twinning was filled with many dislocation lines that exhibited apparent slip systems of climbing and cross-slip. Moreover, the α + β phase with fine dislocation lines and residual twinning were observed in the stress relieving sample. Furthermore, both as-built and stress-relieved samples had a better homogeneous density and finer grains in the center area than in the edge area, displaying good mechanical properties by Feature-Scan. The α’ phase resulted in the improvement of tensile strength and hardness and decrease of plasticity, while the newly generated β phase resulted in a decrease of strength and enhancement of plasticity. The poor plasticity was ascribed to the different print mode, remained support structures and large thermal stresses. Full article
(This article belongs to the Special Issue Additive Manufacturing: Alloy Design and Process Innovations)
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Open AccessArticle Autogenous Shrinkage, Microstructure, and Strength of Ultra-High Performance Concrete Incorporating Carbon Nanofibers
Materials 2019, 12(2), 320; https://doi.org/10.3390/ma12020320
Received: 24 November 2018 / Revised: 30 December 2018 / Accepted: 4 January 2019 / Published: 21 January 2019
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Abstract
The mix design of ultra-high performance concrete (UHPC) is complicated by the presence of many “ingredients.” The fundamental packing density allows a simpler mix design with fewer ingredients to achieve optimum packing density and dense microstructure. The optimum particle grading increases the flowability [...] Read more.
The mix design of ultra-high performance concrete (UHPC) is complicated by the presence of many “ingredients.” The fundamental packing density allows a simpler mix design with fewer ingredients to achieve optimum packing density and dense microstructure. The optimum particle grading increases the flowability of UHPC and eliminates entrapped air. This study presents a simplified particle grading design approach that positively influences the strength, autogenous shrinkage, and microstructure characteristics of UHPC. Carbon nanofibers (CNFs) of superior mechanical properties were added to enhance the strength of UHPC and to reduce its autogenous shrinkage. In addition, ground granulated blast-furnace slag (GGBS) was used as a cement replacement material to reduce the amount of cement in UHPC mixes. Test results showed that the presence of homogeneously dispersed CNF increased the compressive strength and compensated the autogenous shrinkage of UHPC. The findings indicated that an ideal particle distribution, which is close to the modified Andreasen and Andersen grading model, contributed to achieving high compressive strength and CNFs were capable of providing nano-bridges to compensate the shrinkage caused by GGBS. Full article
(This article belongs to the Special Issue New and Emerging Construction Materials)
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Open AccessArticle The Influence of Copper Substrates on Irradiation Effects of Graphene: A Molecular Dynamics Study
Materials 2019, 12(2), 319; https://doi.org/10.3390/ma12020319
Received: 8 December 2018 / Revised: 15 January 2019 / Accepted: 17 January 2019 / Published: 21 January 2019
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Abstract
In this paper, classical molecular dynamics simulations are conducted to study the graphene grown on copper substrates under ion beam irradiation, in which the emphasis is put on the influence copper substrate on a single graphene layer. It can be inferred that the [...] Read more.
In this paper, classical molecular dynamics simulations are conducted to study the graphene grown on copper substrates under ion beam irradiation, in which the emphasis is put on the influence copper substrate on a single graphene layer. It can be inferred that the actual transmission and distribution of kinetic energy from incident ion play important roles in irradiation-defects forming process together. The minimum value needed to generate defects in supported graphene is higher than 2.67 keV, which is almost twice the damage threshold as the suspended graphene sheet. This work indicates the presence of copper substrate increases the damage threshold of graphene. Additionally, our results provide an atomistic explanation for the graphene with copper substrate under ion irradiation, which is very important for engineering graphene. Full article
(This article belongs to the Section Carbon Materials)
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Open AccessArticle Effect of Ti Addition on the Microstructure and Mechanical Properties of SiC Matrix Composites Infiltrated by Al–Si (10 wt.%)–xTi Alloy
Materials 2019, 12(2), 318; https://doi.org/10.3390/ma12020318
Received: 17 December 2018 / Revised: 14 January 2019 / Accepted: 17 January 2019 / Published: 21 January 2019
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This paper proposes a simple reactive melt infiltration process to improve the mechanical properties of silicon carbide (SiC) ceramics. SiC matrix composites were infiltrated by Al–Si (10 wt.%)–xTi melts at 900 °C for 4 h. The effects of Ti addition on the microstructure [...] Read more.
This paper proposes a simple reactive melt infiltration process to improve the mechanical properties of silicon carbide (SiC) ceramics. SiC matrix composites were infiltrated by Al–Si (10 wt.%)–xTi melts at 900 °C for 4 h. The effects of Ti addition on the microstructure and mechanical properties of the composites were investigated. The results showed that the three-point bending strength, fracture toughness (by single-edge notched beam test), and fracture toughness (by Vickers indentation method) of the SiC ceramics increased most by 34.3%, 48.5%, and 128.5%, respectively, following an infiltration with the Al–Si (10 wt.%)–Ti (15 wt.%) melt. A distinct white reaction layer mainly containing a Ti3Si(Al)C2 phase was formed on the surface of the composites infiltrated by Al alloys containing Ti. Ti–Al intermetallic compounds were scattered in the inner regions of the composites. With the increase in the Ti content (from 0 to 15 wt.%) in the Al alloy, the relative contents of Ti3Si(Al)C2 and Ti–Al intermetallic compounds increased. Compared with the fabricated composite infiltrated by an Al alloy without Ti, the fabricated composites infiltrated by Al alloys containing Ti showed improved overall mechanical properties owing to formation of higher relative content Ti3Si(Al)C2 phase and small amounts of Ti–Al intermetallic compounds. Full article
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Open AccessArticle PCSEL Performance of Type-I InGaAsSb Double-QWs Laser Structure Prepared by MBE
Materials 2019, 12(2), 317; https://doi.org/10.3390/ma12020317
Received: 10 December 2018 / Revised: 13 January 2019 / Accepted: 16 January 2019 / Published: 21 January 2019
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This paper discusses the issue of controlling the epitaxial growth of mixed group V alloys to form a type-I InGaAsSb/AlGaAsSb double quantum wells (QWs) structure. We also discuss the run-to-run reproducibility of lattice-matched AlGaAsSb alloys and strained In0.35Ga0.65As0.095 [...] Read more.
This paper discusses the issue of controlling the epitaxial growth of mixed group V alloys to form a type-I InGaAsSb/AlGaAsSb double quantum wells (QWs) structure. We also discuss the run-to-run reproducibility of lattice-matched AlGaAsSb alloys and strained In0.35Ga0.65As0.095Sb0.905 in terms of growth parameters (V/III ratio, Sb2/As2 ratio). Molecular beam epitaxy (MBE) was used to grow two type-I InGaAsSb double-QWs laser structures differing only in the composition of the bottom cladding layer: Al0.85Ga0.15As0.072Sb0.928 (sample A) and Al0.5Ga0.5As0.043Sb0.957 (sample B). Both samples were respectively used in the fabrication of photonic crystal surface-emitting lasers (PCSELs). Sample A presented surface lasing action from circular as well as triangular photonic crystals. Sample B did not present surface lasing due to the deterioration of the active region during the growth of the upper cladding. Our findings underline the importance of temperature in the epitaxial formation of AlxGa1−xAsySb1−y in terms of lasing performance. Full article
(This article belongs to the Section Optics and Photonics)
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Open AccessArticle Study of Structure and Mechanical Properties of Fine-Grained Aluminum Alloys Al-0.6wt.%Mg-Zr-Sc with Ratio Zr:Sc = 1.5 Obtained by Cold Drawing
Materials 2019, 12(2), 316; https://doi.org/10.3390/ma12020316
Received: 4 December 2018 / Revised: 16 January 2019 / Accepted: 17 January 2019 / Published: 21 January 2019
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Abstract
The thermal stability of a fine-grained (FG) aluminum wire has been studied in Al-0.6Mg-Zr-Sc alloys with various scandium and zirconium contents. Specimens were obtained by induction casting followed by cold deformation. The FG alloys have been demonstrated to have high thermal stability of [...] Read more.
The thermal stability of a fine-grained (FG) aluminum wire has been studied in Al-0.6Mg-Zr-Sc alloys with various scandium and zirconium contents. Specimens were obtained by induction casting followed by cold deformation. The FG alloys have been demonstrated to have high thermal stability of the structure and properties due to the annealing pretreatment (320 °C, 2 h, before drawing), which results in deposition of Al3(ScxZr1−x) intermetallic particles. It has been determined that following a prolonged annealing treatment (400 °C, 100 h), the alloys retain a uniform fine-grained structure with an average grain size of 2.4–2.8 μm whereas their microhardness measures 405–440 MPa. Full article
(This article belongs to the Section Structure Analysis and Characterization)
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Open AccessArticle Setting Characteristics, Mechanical Properties and Microstructure of Cement Pastes Containing Accelerators Mixed with Superabsorbent Polymers (SAPs): An NMR Study Combined with Additional Methods
Materials 2019, 12(2), 315; https://doi.org/10.3390/ma12020315
Received: 26 December 2018 / Revised: 9 January 2019 / Accepted: 14 January 2019 / Published: 20 January 2019
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In this study, the setting property and mechanical strength of cement pastes containing accelerators (CPCA) with or without superabsorbent polymers (SAPs) were first studied. The early microstructure evolution and water distribution at 7 and 28 days were probed by 1D (T2 [...] Read more.
In this study, the setting property and mechanical strength of cement pastes containing accelerators (CPCA) with or without superabsorbent polymers (SAPs) were first studied. The early microstructure evolution and water distribution at 7 and 28 days were probed by 1D (T2) and 2D (T1-T2 maps) H1 nuclear magnetic resonance (NMR) relaxometry, and the microstructure was systematically investigated by using mercury intrusion porosimetry (MIP), back-scattered electron (BSE) image and energy-dispersive X-ray spectroscopy (EDX) analysis. Results showed that the SAPs in the cement paste containing accelerators had various influences on setting time and compressive strength depending on the type of accelerators. The presence of SAPs in the cement paste containing alkaline free accelerators could alleviate the decrease of internal relative humidity, promote hydration and help to modify the pore structure. Moreover, it was observed that the SAP cavities could be nicely filled with calcium hydroxide (CH) in the cement paste with alkaline free accelerators. Full article
(This article belongs to the Section Structure Analysis and Characterization)
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Open AccessReview A Precautionary Approach to Guide the Use of Transition Metal-Based Nanotechnology to Prevent Orthopedic Infections
Materials 2019, 12(2), 314; https://doi.org/10.3390/ma12020314
Received: 6 December 2018 / Revised: 15 January 2019 / Accepted: 18 January 2019 / Published: 20 January 2019
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Abstract
The increase of multidrug-resistant bacteria remains a global concern. Among the proposed strategies, the use of nanoparticles (NPs) alone or associated with orthopedic implants represents a promising solution. NPs are well-known for their antimicrobial effects, induced by their size, shape, charge, concentration and [...] Read more.
The increase of multidrug-resistant bacteria remains a global concern. Among the proposed strategies, the use of nanoparticles (NPs) alone or associated with orthopedic implants represents a promising solution. NPs are well-known for their antimicrobial effects, induced by their size, shape, charge, concentration and reactive oxygen species (ROS) generation. However, this non-specific cytotoxic potential is a powerful weapon effective against almost all microorganisms, but also against eukaryotic cells, raising concerns related to their safe use. Among the analyzed transition metals, silver is the most investigated element due to its antimicrobial properties per se or as NPs; however, its toxicity raises questions about its biosafety. Even though it has milder antimicrobial and cytotoxic activity, TiO2 needs to be exposed to UV light to be activated, thus limiting its use conjugated to orthopedic devices. By contrast, gold has a good balance between antimicrobial activity as an NP and cytocompatibility because of its inability to generate ROS. Nevertheless, although the toxicity and persistence of NPs within filter organs are not well verified, nowadays, several basic research on NP development and potential uses as antimicrobial weapons is reported, overemphasizing NPs potentialities, but without any existing potential of translation in clinics. This analysis cautions readers with respect to regulation in advancing the development and use of NPs. Hopefully, future works in vivo and clinical trials will support and regulate the use of nano-coatings to guarantee safer use of this promising approach against antibiotic-resistant microorganisms. Full article
(This article belongs to the Special Issue Antimicrobial Nanomaterials)
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Open AccessArticle Effect of Lubricating Phase on Microstructure and Properties of Cu–Fe Friction Materials
Materials 2019, 12(2), 313; https://doi.org/10.3390/ma12020313
Received: 17 December 2018 / Revised: 11 January 2019 / Accepted: 15 January 2019 / Published: 20 January 2019
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Abstract
Cu–Fe-based friction materials with flake graphite, granulated carbon black, and high-strength graphite as lubricating phase were prepared by the powder metallurgy method. The effects of different types and mass fraction of lubricating phase on the microstructure, mechanical properties, and tribological properties were investigated. [...] Read more.
Cu–Fe-based friction materials with flake graphite, granulated carbon black, and high-strength graphite as lubricating phase were prepared by the powder metallurgy method. The effects of different types and mass fraction of lubricating phase on the microstructure, mechanical properties, and tribological properties were investigated. The results show that when the mass fraction of granulated carbon black is 5 wt%, it is easy to form a good interface with the matrix, but the interface is prone to pores and cracks when its mass fraction is 10 wt%. The bending strength and compressive strength properties of the composites increased with increasing in the mass fraction of granulated carbon black and reached the maximum of 40 MPa and 70 MPa at 5 wt% granulated carbon black, after which bending strength and compressive strength all decreased. The friction coefficient and the wear loss of the materials initially decreased as the mass fraction of granulated carbon black increased and obtained minimum of 0.436 and 0.145 mm when the mass fraction of granulated carbon black was 5 wt%, then ascended. Compared with the sample with 5 wt% high-strength graphite as lubricating phase, the sample with 5 wt% granulated carbon black as lubricating phase had better sintering performance, mechanical properties, and tribological properties. Full article
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Open AccessArticle Development of a New Ultra-High-Precision Magnetic Abrasive Finishing for Wire Material Using a Rotating Magnetic Field
Materials 2019, 12(2), 312; https://doi.org/10.3390/ma12020312
Received: 17 December 2018 / Revised: 14 January 2019 / Accepted: 15 January 2019 / Published: 20 January 2019
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Abstract
In this paper, we propose a new ultra-high-precision magnetic abrasive finishing method for wire material which is considered to be difficult with the existing finishing process. The processing method uses a rotating magnetic field system with unbonded magnetic abrasive type. It is believed [...] Read more.
In this paper, we propose a new ultra-high-precision magnetic abrasive finishing method for wire material which is considered to be difficult with the existing finishing process. The processing method uses a rotating magnetic field system with unbonded magnetic abrasive type. It is believed that this process can efficiently perform the ultra-high-precision finishing for producing a smooth surface finish and removing a diameter of wire material. For such a processing improvement, the following parameters are considered; rotational speed of rotating magnetic field, vibration frequency of wire material, and unbonded magnetic abrasive grain size. In order to evaluate the performance of the new finishing process for the wire material, the American Iron and Steel Institute (AISI) 1085 steel wire was used as the wire workpiece. The experimental results showed that the original surface roughness of AISI 1085 steel wire was enhanced from 0.25 µm to 0.02 µm for 60 s at 800 rpm of rotational speed. Also, the performance of the removed diameter was excellent. As the result, a new ultra-high-precision magnetic abrasive finishing using a rotating magnetic field with unbonded magnetic abrasive type could be successfully adopted for improving the surface roughness and removing the diameter of AISI 1085 steel wire material. Full article
(This article belongs to the Section Manufacturing Processes and Systems)
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Open AccessArticle Effect of Heat Treatment Condition on the Flow Behavior and Recrystallization Mechanisms of Aluminum Alloy 7055
Materials 2019, 12(2), 311; https://doi.org/10.3390/ma12020311
Received: 9 December 2018 / Revised: 11 January 2019 / Accepted: 14 January 2019 / Published: 20 January 2019
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Abstract
The flow behavior and the microstructural evolution of aluminum alloy 7055 in two heat treatment conditions (homogenized vs. pre-rolled, solution treated, stretched and naturally aged (T3)) were investigated for a height reduction of 60% with deformation temperatures ranging from 370 °C to 450 [...] Read more.
The flow behavior and the microstructural evolution of aluminum alloy 7055 in two heat treatment conditions (homogenized vs. pre-rolled, solution treated, stretched and naturally aged (T3)) were investigated for a height reduction of 60% with deformation temperatures ranging from 370 °C to 450 °C and strain rates ranging from 0.01 s−1 to 10 s−1. Flow stress decline ratio maps as a function of deformation temperature and strain rate were produced along with processing maps at a strain of 0.8 to reveal optimum hot-working conditions for deformation at strain rates of 0.01 s−1 to 0.1 s−1. The results showed that the stress drop ratio during deformation is higher for the homogenized condition than for the pre-rolled, T3 condition. A higher degree of recrystallization after deformation was observed in the pre-rolled, T3 condition due to finer second phase particles, smaller grain size, and more numerous sub-grains. The mechanism for deformation softening is discussed in the context of grain boundary characteristics. Full article
(This article belongs to the Special Issue Advanced Metal Forming Processes)
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Open AccessArticle Quantifying Joule Heating and Mass Transport in Metal Nanowires during Controlled Electromigration
Materials 2019, 12(2), 310; https://doi.org/10.3390/ma12020310
Received: 30 December 2018 / Revised: 15 January 2019 / Accepted: 15 January 2019 / Published: 19 January 2019
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Abstract
The nanoscale heat dissipation (Joule heating) and mass transport during electromigration (EM) have attracted considerable attention in recent years. Here, the EM-driven movement of voids in gold (Au) nanowires of different shapes (width range: 50–300 nm) was directly observed by performing atomic force [...] Read more.
The nanoscale heat dissipation (Joule heating) and mass transport during electromigration (EM) have attracted considerable attention in recent years. Here, the EM-driven movement of voids in gold (Au) nanowires of different shapes (width range: 50–300 nm) was directly observed by performing atomic force microscopy. Using the data, we determined the average mass transport rate to be 105 to 106 atoms/s. We investigated the heat dissipation in L-shaped, straight-shaped, and bowtie-shaped nanowires. The maximum Joule heating power of the straight-shaped nanowires was three times that of the bowtie-shaped nanowires, indicating that EM in the latter can be triggered by lower power. Based on the power dissipated by the nanowires, the local temperature during EM was estimated. Both the local temperature and junction voltage of the bowtie-shaped nanowires increased with the decrease in the Joule heating power and current, while the current density remained in the order of 108 A/cm2. The straight-shaped nanowires exhibited the same tendency. The local temperature at each feedback point could be simply estimated using the diffusive heat transport relationship. These results suggest that the EM-driven mass transport can be controlled at temperatures much lower than the melting point of Au. Full article
(This article belongs to the Special Issue Metallic Nanowires and Their Applications)
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Open AccessArticle Preparation of La0.7Ca0.3−xSrxMnO3 Manganites by Four Synthesis Methods and Their Influence on the Magnetic Properties and Relative Cooling Power
Materials 2019, 12(2), 309; https://doi.org/10.3390/ma12020309
Received: 19 December 2018 / Revised: 11 January 2019 / Accepted: 17 January 2019 / Published: 19 January 2019
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Abstract
Manganites of the family La0.7Ca0.3−xSrxMnO3 were fabricated by four preparation methods: (a) the microwave-assisted sol-gel Pechini method; (b) sol-gel Pechini chemical synthesis; (c) solid-state reaction with a planetary mill; and (d) solid-state reaction with an attritor [...] Read more.
Manganites of the family La0.7Ca0.3−xSrxMnO3 were fabricated by four preparation methods: (a) the microwave-assisted sol-gel Pechini method; (b) sol-gel Pechini chemical synthesis; (c) solid-state reaction with a planetary mill; and (d) solid-state reaction with an attritor mill, in order to study the effect of the preparation route used on its magnetocaloric and magnetic properties. In addition, the manganites manufactured by the Pechini sol-gel method were compacted using Spark Plasma Sintering (SPS) to determine how the consolidation process influences its magnetocaloric properties. The Curie temperatures of manganites prepared by the different methods were determined in ~295 K, with the exception of those prepared by a solid-state reaction with an attritor mill which was 301 K, so there is no correlation between the particle size and the Curie temperature. All samples gave a positive slope in the Arrot plots, which implies that the samples underwent a second order Ferromagnetic (FM)–Paramagnetic (PM) phase transition. Pechini sol-gel manganite presents higher values of Relative Cooling Power (RCP) than the solid-state reaction manganite, because its entropy change curves are smaller, but wider, associated to the particle size obtained by the preparation method. The SPS technique proved to be easier and faster in producing consolidated solids for applications in active magnetic regenerative refrigeration compared with other compaction methods. Full article
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Open AccessArticle Analysis of Melt Pool Characteristics and Process Parameters Using a Coaxial Monitoring System during Directed Energy Deposition in Additive Manufacturing
Materials 2019, 12(2), 308; https://doi.org/10.3390/ma12020308
Received: 10 December 2018 / Revised: 11 January 2019 / Accepted: 12 January 2019 / Published: 19 January 2019
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Abstract
The growing number of commercially available machines for laser deposition welding show the growing acceptance and importance of this technology for industrial applications. Their increasing usage in research and production requires process stability and user-friendly handling. A commercially available DMG MORI LT 65 [...] Read more.
The growing number of commercially available machines for laser deposition welding show the growing acceptance and importance of this technology for industrial applications. Their increasing usage in research and production requires process stability and user-friendly handling. A commercially available DMG MORI LT 65 3D hybrid machine used in combination with a CCD-based coaxial temperature measurement system was utilized in this work to investigate what information relating to the intensity distribution of melt pool surfaces could be appropriate to draw conclusions about process conditions. In this study it is shown how the minimal required specific energy for a stable process can be determined, and it is indicated that the evolution of a plasma plume depends on thermal energy within the base material. An estimated melt pool area—calculated by the number of pixels (NOP) with intensities larger than a fixed, predefined threshold—builds the main measure in analysing images from the process camera. The melt pool area and its temporal variance can also serve as an indicator for an increased working distance. Full article
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Open AccessArticle Inhibitive Properties of Benzyldimethyldodecylammonium Chloride on Microbial Corrosion of 304 Stainless Steel in a Desulfovibrio desulfuricans-Inoculated Medium
Materials 2019, 12(2), 307; https://doi.org/10.3390/ma12020307
Received: 13 December 2018 / Revised: 16 January 2019 / Accepted: 17 January 2019 / Published: 18 January 2019
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Abstract
Biocides are frequently used to control sulfate-reducing bacteria (SRB) in biofouling. The increasing restrictions of environmental regulations and growing safety concerns on the use of biocides result in efforts to minimize the amount of biocide use and develop environmentally friendly biocides. In this [...] Read more.
Biocides are frequently used to control sulfate-reducing bacteria (SRB) in biofouling. The increasing restrictions of environmental regulations and growing safety concerns on the use of biocides result in efforts to minimize the amount of biocide use and develop environmentally friendly biocides. In this study, the antimicrobial activity and corrosion inhibition effect of a low-toxic alternative biocide, benzyldimethyldodecylammonium chloride (BDMDAC), on a 304 stainless steel substrate immersed in a Desulfovibrio desulfuricans (D. desulfuricans)-inoculated medium was examined. Potentiodynamic polarization curves were used to analyze corrosion behavior. Biofilm formation and corrosion products on the surfaces of 304 stainless steel coupons were examined using scanning electron microscopy (SEM), energy-dispersive X-ray spectrum, and confocal laser scanning microscopy (CLSM). Results demonstrated that this compound exhibited satisfactory results against microbial corrosion by D. desulfuricans. The corrosion current density and current densities in the anodic region were lower in the presence of BDMDAC in the D. desulfuricans-inoculated medium. SEM and CLSM analyses revealed that the presence of BDMDAC mitigated formation of biofilm by D. desulfuricans. Full article
(This article belongs to the Special Issue Corrosion and Protection of Materials)
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Open AccessArticle Electrolyte-Supported Fuel Cell: Co-Sintering Effects of Layer Deposition on Biaxial Strength
Materials 2019, 12(2), 306; https://doi.org/10.3390/ma12020306
Received: 13 December 2018 / Revised: 11 January 2019 / Accepted: 15 January 2019 / Published: 18 January 2019
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Abstract
The mechanical reliability of reversible solid oxide cell (SOC) components is critical for the development of highly efficient, durable, and commercially competitive devices. In particular, the mechanical integrity of the ceramic cell, also known as membrane electrolyte assembly (MEA), is fundamental as its [...] Read more.
The mechanical reliability of reversible solid oxide cell (SOC) components is critical for the development of highly efficient, durable, and commercially competitive devices. In particular, the mechanical integrity of the ceramic cell, also known as membrane electrolyte assembly (MEA), is fundamental as its failure would be detrimental to the performance of the whole SOC stack. In the present work, the mechanical robustness of an electrolyte-supported cell was determined via ball-on-3-balls flexural strength measurements. The main focus was to investigate the effect of the manufacturing process (i.e., layer by layer deposition and their co-sintering) on the final strength. To allow this investigation, the electrode layers were screen-printed one by one on the electrolyte support and thus sintered. Strength tests were performed after every layer deposition and the non-symmetrical layout was taken into account during mechanical testing. Obtained experimental data were evaluated with the help of Weibull statistical analysis. A loss of mechanical strength after every layer deposition was usually detected, with the final strength of the cell being significantly smaller than the initial strength of the uncoated electrolyte (σ0 ≈ 800 MPa and σ0 ≈ 1800 MPa, respectively). Fractographic analyses helped to reveal the fracture behavior changes when individual layers were deposited. It was found that the reasons behind the weakening effect can be ascribed to the presence and redistribution of residual stresses, changes in the crack initiation site, porosity of layers, and pre-crack formation in the electrode layers. Full article
(This article belongs to the Special Issue Advanced Glasses, Composites and Ceramics for High Growth Industries)
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Open AccessArticle A Comparison of Ethylene-Tar-Derived Isotropic Pitches Prepared by Air Blowing and Nitrogen Distillation Methods and Their Carbon Fibers
Materials 2019, 12(2), 305; https://doi.org/10.3390/ma12020305
Received: 7 December 2018 / Revised: 15 January 2019 / Accepted: 15 January 2019 / Published: 18 January 2019
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Abstract
Two isotropic pitches were prepared by air blowing and nitrogen distillation methods using ethylene tar (ET) as a raw material. The corresponding carbon fibers were obtained through conventional melt spinning, stabilization, and carbonization. The structures and properties of the resultant pitches and fibers [...] Read more.
Two isotropic pitches were prepared by air blowing and nitrogen distillation methods using ethylene tar (ET) as a raw material. The corresponding carbon fibers were obtained through conventional melt spinning, stabilization, and carbonization. The structures and properties of the resultant pitches and fibers were characterized, and their differences were examined. The results showed that the introduction of oxygen by the air blowing method could quickly increase the yield and the softening point of the pitch. Moreover, the air-blown pitch (ABP) was composed of aromatic molecules with linear methylene chains, while the nitrogen-distilled pitch (NDP) mainly contained polycondensed aromatic rings. This is because the oxygen-containing functional groups in the ABP could impede ordered stack of pitch molecules and led to a methylene bridge structure instead of an aromatic condensed structure as in the NDP. Meanwhile, the spinnability of the ABP did not decrease even though it contained 2.31 wt % oxygen. In contrast, the ABP had narrower molecular weight distribution, which contributed to better stabilization properties and higher tensile strength of the carbon fiber. The tensile strength of carbon fibers from the ABP reached 860 MPa with fiber diameter of about 10 μm, which was higher than the tensile strength of 640 MPa for the NDP-derived carbon fibers. Full article
(This article belongs to the Special Issue Carbon Fibers and Their Composite Materials)
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Open AccessReview Synthesis of Structurally Precise Polysiloxanes via the Piers–Rubinsztajn Reaction
Materials 2019, 12(2), 304; https://doi.org/10.3390/ma12020304
Received: 7 December 2018 / Revised: 8 January 2019 / Accepted: 15 January 2019 / Published: 18 January 2019
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Abstract
Silicone materials are widely used, from daily life to the military industry. With the advancement of science and technology and the increasing demands of industry, the requirement for high-performance precise structural silicone materials has increased. Therefore, the most important aspect in this field [...] Read more.
Silicone materials are widely used, from daily life to the military industry. With the advancement of science and technology and the increasing demands of industry, the requirement for high-performance precise structural silicone materials has increased. Therefore, the most important aspect in this field is finding a breakthrough in the synthetic methods. In this review, the latest research developments in controllable morphological structure and composite structure optimized synthesis of silicone materials using the Piers–Rubinsztajn (PR) reaction are summarized. The advantages of the PR reaction compared with traditional synthetic routes to silicone materials are presented. The highly controllable spatial structure of silicone materials and the structural combination of biomass or inorganic materials with silicone materials results in an improvement in performance or function. The morphological control of more complex silicone materials and the synthesis of non-traditional silicone materials with composite structures through the PR reaction will be the main research directions for the development of silicone materials in the future. Full article
(This article belongs to the Section Materials Chemistry)
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Open AccessArticle Experimental Studies on Chemical Activation of Cementitious Materials from Smelting Slag of Copper and Nickel Mine
Materials 2019, 12(2), 303; https://doi.org/10.3390/ma12020303
Received: 18 December 2018 / Revised: 11 January 2019 / Accepted: 17 January 2019 / Published: 18 January 2019
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Abstract
Gellable composite materials (GCM) were prepared from a smelting slag of copper and nickel deposits and cement, and activated using gypsum and chemical activators. The effects of material ratio, dosage of chemical activators, and gypsum on the mechanical properties of GCM were studied. [...] Read more.
Gellable composite materials (GCM) were prepared from a smelting slag of copper and nickel deposits and cement, and activated using gypsum and chemical activators. The effects of material ratio, dosage of chemical activators, and gypsum on the mechanical properties of GCM were studied. Our results showed that the chemical activators of Na2SO4, Na2SiO3, NaOH, and Na2CO3 could improve the compressive strength of the GCM. Considering the market cost and ease operation, the compressive strength of the GCM could be significantly improved with 2% Na2SO4. The experiment results also showed that the compound chemical activator could improve the compressive strength of gelled material. The strength of GCM reaches 41.6 MPa when 2% gypsum and 80% of smelting slags of copper and nickel deposits were used, which met the national standards requirements of GCM. As such, it is expected that a large amount of copper and nickel mining smelting slag could be utilized for the production of cementitious materials. Full article
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Open AccessArticle The Effect of UV Illumination on the Room Temperature Detection of Vaporized Ammonium Nitrate by a ZnO Coated Nanospring-Based Sensor
Materials 2019, 12(2), 302; https://doi.org/10.3390/ma12020302
Received: 13 December 2018 / Revised: 9 January 2019 / Accepted: 16 January 2019 / Published: 18 January 2019
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Abstract
The effect of UV illumination on the room temperature electrical detection of ammonium nitrate vapor was examined. The sensor consists of a self-assembled ensemble of silica nanosprings coated with zinc oxide. UV illumination mitigates the baseline drift of the resistance relative to operation [...] Read more.
The effect of UV illumination on the room temperature electrical detection of ammonium nitrate vapor was examined. The sensor consists of a self-assembled ensemble of silica nanosprings coated with zinc oxide. UV illumination mitigates the baseline drift of the resistance relative to operation under dark conditions. It also lowers the baseline resistance of the sensor by 25% compared to dark conditions. At high ammonium nitrate concentrations (120 ppm), the recovery time after exposure is virtually identical with or without UV illumination. At low ammonium nitrate concentrations (20 ppm), UV illumination assists with refreshing of the sensor by stimulating analyte desorption, thereby enabling the sensor to return to its baseline resistance. Under dark conditions and low ammonium nitrate concentrations, residual analyte builds up with each exposure, which inhibits the sensor from returning to its original baseline resistance and subsequently impedes sensing due to permanent occupation of absorption sites. Full article
(This article belongs to the Special Issue ZnO-Based Nanomaterials and Devices: Fundamentals and Applications)
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